Laminated glass including two glass plates integrated through an interlayer film for a laminated glass containing a plasticized polyvinyl acetal is widely used as glass for vehicles including cars and aircraft and window glass of buildings or the like. Laminated glass can prevent scattering of glass pieces or infliction of damage by glass pieces to human bodies or instruments upon collision of an object with the glass.
Upon lamination of an interlayer film for a laminated glass and a glass plate in production of a laminated glass, an excess of the interlayer film for a laminated glass at an end portion is cut off, and a large amount of such an excess interlayer film for a laminated glass is discarded.
Laminated glass used for automobiles or aircraft needs to meet a very strict standard for quality, and those containing cells entrapped upon lamination are considered as defective products. In particular, in the case of large-area windshields, such entrapment of cells is likely to occur, and therefore, a huge amount of defective products presumably occurs in consideration of the amount of the laminated glass used in the world.
Moreover, upon scrapping the used laminated glass, a large amount of interlayer films for a laminated glass is collected and discarded.
Such a large quantity of waste interlayer films for a laminated glass is demanded to be reused from the standpoint of recycling or the like.
To meet this demand, reuse of interlayer films for a laminated glass, i.e., reuse of a plasticized polyvinyl acetal is also attempted. For example, Patent Literature 1 discloses a method of producing a foamed article by heating a mixture of polyvinyl butyral and a specific heat-decomposable foaming agent to decompose the heat-decomposable foaming agent. However, such a foamed article of a plasticized polyvinyl acetal is not particularly excellent in shock absorption and applications thereof are limited.
Accordingly, establishment of an effective recycle system of interlayer films for a laminated glass is an urgent need.